Jón Ólafsson

Genetic determinants of hair, eye and skin pigmentation in Europeans

Hair, skin and eye colors are highly heritable and visible traits in humans. We carried out a genome-wide association scan for variants associated with hair and eye pigmentation, skin sensitivity to sun and freckling among 2,986 Icelanders. We then tested the most closely associated SNPs from six regions—four not previously implicated in the normal variation of human pigmentation—and replicated their association in a second sample of 2,718 Icelanders and a sample of 1,214 Dutch. The SNPs from all six regions met the criteria for genome-wide significance. A variant in SLC24A4 is associated with eye and hair color, a variant near KITLG is associated with hair color, two coding variants in TYR are associated with eye color and freckles, and a variant on 6p25.3 is associated with freckles. The fifth region provided refinements to a previously reported association in OCA2, and the sixth encompasses previously described variants in MC1R.

Sequence variants at the TERT-CLPTM1L locus associate with many cancer types

The common sequence variants that have recently been associated with cancer risk are particular to a single cancer type or at most two. Following up on our genome-wide scan of basal cell carcinoma, we found that rs401681[C] on chromosome 5p15.33 satisfied our threshold for genome-wide significance (OR = 1.25, P = 3.7 × 10−12). We tested rs401681 for association with 16 additional cancer types in over 30,000 cancer cases and 45,000 controls and found association with lung cancer (OR = 1.15, P = 7.2 × 10−8) and urinary bladder, prostate and cervix cancer (ORs = 1.07−1.31, all P < 4 × 10−4). However, rs401681[C] seems to confer protection against cutaneous melanoma (OR = 0.88, P = 8.0 × 10−4). Notably, most of these cancer types have a strong environmental component to their risk. Investigation of the region led us to rs2736098[A], which showed stronger association with some cancer types. However, neither variant could fully account for the association of the other. rs2736098 corresponds to A305A in the telomerase reverse transcriptase (TERT) protein and rs401681 is in an intron of the CLPTM1L gene.

Parental origin of sequence variants associated with complex diseases.

Effects of susceptibility variants may depend on from which parent they are inherited. Although many associations between sequence variants and human traits have been discovered through genome-wide associations, the impact of parental origin has largely been ignored. Here we show that for 38,167 Icelanders genotyped using single nucleotide polymorphism (SNP) chips, the parental origin of most alleles can be determined. For this we used a combination of genealogy and long-range phasing. We then focused on SNPs that associate with diseases and are within 500 kilobases of known imprinted genes. Seven independent SNP associations were examined. Five—one with breast cancer, one with basal-cell carcinoma and three with type 2 diabetes—have parental-origin-specific associations. These variants are located in two genomic regions, 11p15 and 7q32, each harbouring a cluster of imprinted genes. Furthermore, we observed a novel association between the SNP rs2334499 at 11p15 and type 2 diabetes. Here the allele that confers risk when paternally inherited is protective when maternally transmitted. We identified a differentially methylated CTCF-binding site at 11p15 and demonstrated correlation of rs2334499 with decreased methylation of that site.

ASIP and TYR pigmentation variants associate with cutaneous melanoma and basal cell carcinoma

Fair color increases risk of cutaneous melanoma (CM) and basal cell carcinoma (BCC). Recent genome-wide association studies have identified variants affecting hair, eye and skin pigmentation in Europeans. Here, we assess the effect of these variants on risk of CM and BCC in European populations comprising 2,121 individuals with CM, 2,163 individuals with BCC and over 40,000 controls. A haplotype near ASIP, known to affect a similar spectrum of pigmentation traits as MC1R variants, conferred significant risk of CM (odds ratio (OR) = 1.45, P = 1.2 × 10−9) and BCC (OR = 1.35, P = 1.2 × 10−6). The variant in TYR encoding the R402Q amino acid substitution, previously shown to affect eye color and tanning response, conferred risk of CM (OR = 1.21, P = 2.8 × 10−7) and BCC (OR = 1.14, P = 6.1 × 10−4). An eye color variant in TYRP1 was associated with risk of CM (OR = 1.15, P = 4.3 × 10−4). The association of all three variants is robust with respect to adjustment for the effect of pigmentation.

New common variants affecting susceptibility to basal cell carcinoma

In a follow-up to our previously reported genome-wide association study of cutaneous basal cell carcinoma (BCC), we describe here several new susceptibility variants. SNP rs11170164, encoding a G138E substitution in the keratin 5 (KRT5) gene, affects risk of BCC (OR = 1.35, P = 2.1 × 10−9). A variant at 9p21 near CDKN2A and CDKN2B also confers susceptibility to BCC (rs2151280[C]; OR = 1.19, P = 6.9 × 10−9), as does rs157935[T] at 7q32 near the imprinted gene KLF14 (OR = 1.23, P = 5.7 × 10−10). The effect of rs157935[T] is dependent on the parental origin of the risk allele. None of these variants were found to be associated with melanoma or fair-pigmentation traits. A melanoma- and pigmentation-associated variant in the SLC45A2 gene, L374F, is associated with risk of both BCC and squamous cell carcinoma. Finally, we report conclusive evidence that rs401681[C] in the TERT-CLPTM1L locus confers susceptibility to BCC but protects against melanoma.

Two newly identified genetic determinants of pigmentation in Europeans.

We present results from a genome-wide association study for variants associated with human pigmentation characteristics among 5,130 Icelanders, with follow-up analyses in 2,116 Icelanders and 1,214 Dutch individuals. Two coding variants in TPCN2 are associated with hair color, and a variant at the ASIP locus shows strong association with skin sensitivity to sun, freckling and red hair, phenotypic characteristics similar to those affected by well-known mutations in MC1R.

Common variants on 1p36 and 1q42 are associated with cutaneous basal cell carcinoma but not with melanoma or pigmentation traits

To search for new sequence variants that confer risk of cutaneous basal cell carcinoma (BCC), we conducted a genome-wide SNP association study of 930 Icelanders with BCC and 33,117 controls. After analyzing 304,083 SNPs, we observed signals from loci at 1p36 and 1q42, and replicated these associations in additional sample sets from Iceland and Eastern Europe. Overall, the most significant signals were from rs7538876 on 1p36 (OR = 1.28, P = 4.4 × 10−12) and rs801114 on 1q42 (OR = 1.28, P = 5.9 × 10−12). The 1p36 locus contains the candidate genes PADI4, PADI6, RCC2 and ARHGEF10L, and the gene nearest to the 1q42 locus is the ras-homolog RHOU. Neither locus was associated with fair pigmentation traits that are known risk factors for BCC, and no risk was observed for melanoma. Approximately 1.6% of individuals of European ancestry are homozygous for both variants, and their estimated risk of BCC is 2.68 times that of noncarriers.

A Melanoma Epidemic in Iceland: Possible Influence of Sunbed Use

Since 1980, sunbed use and travel abroad have dramatically increased in Iceland (64°-66°N). The authors assessed temporal trends in melanoma incidence by body site in Iceland in relation to sunbed use and travel abroad. Using joinpoint analysis, they calculated estimated annual percent changes (EAPCs) and identified the years during which statistically significant changes in EAPC occurred. Between 1954 and 2006, the largest increase in incidence in men was observed on the trunk (EAPC = 4.6%, 95% confidence interval: 3.2, 6.0). In women, the slow increase in trunk melanoma incidence before 1995 was followed by a significantly sharper increase in incidence, mainly among women aged less than 50 years, resembling an epidemic incidence curve (1995-2002: EAPC = 20.4%, 95% confidence interval: 9.3, 32.8). In 2002, the melanoma incidence on the trunk was higher than the incidence on the lower limbs for women. Sunbed use in Iceland expanded rapidly after 1985, mainly among young women, and in 2000, it was approximately 2 and 3 times the levels recorded in Sweden and in the United Kingdom, respectively. Travels abroad were more prevalent among older Icelanders. The high prevalence of sunbed use probably contributed to the sharp increase in the incidence of melanoma in Iceland.

A variant in FTO shows association with melanoma risk not due to BMI

We report the results of an association study of melanoma that is based on the genome-wide imputation of the genotypes of 1,353 cases and 3,566 controls of European origin conducted by the GenoMEL consortium. This revealed an association between several SNPs in intron 8 of the FTO gene, including rs16953002, which replicated using 12,313 cases and 55,667 controls of European ancestry from Europe, the USA and Australia (combined P = 3.6 × 10−12, per-allele odds ratio for allele A = 1.16). In addition to identifying a new melanoma-susceptibility locus, this is to our knowledge the first study to identify and replicate an association with SNPs in FTO not related to body mass index (BMI). These SNPs are not in intron 1 (the BMI-related region) and exhibit no association with BMI. This suggests FTOs function may be broader than the existing paradigm that FTO variants influence multiple traits only through their associations with BMI and obesity.

Improvement of Psoriasis after Tonsillectomy Is Associated with a Decrease in the Frequency of Circulating T Cells That Recognize Streptococcal Determinants and Homologous Skin Determinants

Exacerbation of chronic psoriasis can be associated with streptococcal throat infections, and T cells that respond to peptide sequences common to streptococcal M proteins and skin keratins have been detected in patients’ blood. To our knowledge, we have conducted the first blinded, prospective study to assess the impact of tonsillectomy on psoriasis. Twenty-nine patients with chronic psoriasis and history of exacerbation after sore throat were randomly assigned to tonsillectomy (n = 15) or control (n = 14) groups and monitored for 2 y clinically and by enumeration of circulating skin homing T cells that respond to short homologous M protein or keratin peptides. Thirteen patients (86%) showed sustained improvement after tonsillectomy ranging from 30 to 90% reduction in disease severity. Furthermore, there was a close correlation between the degree of clinical improvement in individual patients and reduction in the frequency of peptide-reactive skin-homing T cells in their circulation. No corresponding clinical or immunologic changes were observed among the controls. These findings indicate that tonsillectomy may have a beneficial effect on chronic psoriasis because the palatine tonsils generate effector T cells that recognize keratin determinants in the skin.